1. Field of the Disclosure
The instant disclosure relates to an output-stage circuit: in particular, to an over-current protection method of the output-stage circuit.
2. Description of Related Art
In recent years, considering technology of semiconductor is getting more mature and portable consumer electronics devices are getting wide popularity, how to design an audio amplifier has become an important research topic. Generally speaking, an output-stage circuit is consisted of a high-side output driver and a low-side output driver, and the high-side output driver devices and low-side output driver device are respectively connected to the body selector to prevent a speaker from making a clicking sound, wherein the high-side output driver is a high-side P-type power transistor, and the low-side output driver is a low-side N-type power transistor. Regarding cause and control of the clicking sound, there is reference in content of disclosure in U.S. Pat. No. 7,265,614.
Generally speaking, an audio amplifier utilizes a load, such as a speaker, through an output-stage circuit. Once the current flowing through is larger than an affordable value of the high-side P-type power transistor or the low-side N-type power transistor, there will be an over-current fault, wherein there are a lot causes of the over-current fault, such as a short circuit or a spiking voltage. The faults may hurt the high-side P-type power transistor or the low-side N-type power transistor seriously and permanently, and further lead to a damage to the entire audio circuit. For example, in prior art, when an output current flowing into a body selector through the high-side P-type power transistor to release the output current, the spiking voltage of the output voltage will be too high because of a body diode inside of the high-side P-type power transistor and the body selector; on the other hand, when the output current flowing into another body selector through the low-side N-type transistor to release an output current, the spiking voltage of the output voltage will be too low because of a body diode inside of the N-type transistor and the body selector.
Therefore, how to avoid sudden arising current from damaging circuit elements becomes a problem for an audio circuit design.